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<br />Robichaud, P.R., 1996, Spatially-varied erosion potential from harvested hillslopes <br />after prescribed fire in the interior northwest: Moscow, University of Idaho, <br />Ph.D. dissertation, 219 p. <br />A section of this dissertation is devoted to the study of water-repellent soils, as part of a <br />broader investigation into the effects of post-fire, spatially-varied surface conditions on <br />erosion. Included is a comprehensive literature review on water repellency, as well as the <br />author's own investigation into the formation of water-repellent conditions with respect to <br />texture and moisture content at the time of burning. The study consisted of exposing four <br />textures of soils to four levels of heating at low and high moisture contents, and then <br />measuring the resultant water repellencies at various depths. Unlike most research on water- <br />repellent soils, this study included experiments using volcanic ash-derived soils; a topic that <br />the author notes, has received little attention. Results were quite variable. <br /> <br />Salih, M.S.A., Taha, F.K., and Payne, G.F., 1973, Water repellency of soils under <br />burned sagebrush: Journal of Range Management, V.26, no.5, p. 300-331. <br />Results of laboratory and fIeld testing demonstrates that the burning of sagebrush produces <br />water repellency in soils. Field tests indicate that water repellency is produced as a result of <br />the burning of the sagebrush leaf mulch under the shrub, rather than the burning of the live <br />plant material. Maximum repellency occurs at soil temperatures between 1400 and 1800 <br />degrees F. <br /> <br />Savage, S.M., 1974, Mechanism of fire-induced water repellency in soil: Soil Science <br />Society of America Proceedings, v. 38, p. 652-657. <br />Chaparral (manzanita) litter from the Red Mountain area in southern California was <br />subjected to two types laboratory bum experiments over a sand column. In the fIrst <br />experiment, the burned litter remained on the surface of the sand, while in the second <br />experiment, the litter was removed after burning to prevent heat in the litter from moving <br />into the sand. The latter resulted in lower maximum soil temperatures and less severe water <br />repellency. Following bum treatments, materials were extracted from the water-repellent <br />sand and subjected to fractionation analysis. Results indicated that molecules of the <br />hydrophobic substances showed a decrease in polarity with depth in the sand column. The <br />author concludes that organic substances from the litter layer probably move into the <br />underlying sand during the fire, and confer a mild repellency as they condense on cooler soil <br />particles at a shallow depth. Subsequent heat from the litter layer (after burning) moves into <br />the sand and "fIxes" the polar hydrophobic substances in place, while the less polar ones <br />migrate deeper into the soil, thus increasing the thickness of the water-repellent layer. The <br />author points out that this process, which is controlled by the intensity of the heat moving <br />down into the soil prof1le, governs the thickness of the water-repellent layer (along with soil <br />texture, as reported by other researchers). The author also suggests that the amount of <br />hydrophobic substances initially produced by the litter depends on the duration and intensity <br />of the fire and the quantity of litter in the soil. The introduction includes a literature review <br />of previous research into the causes of fire-related water repellency. <br /> <br />33 <br />